In fact, ReactOS maintains a policy to prevent proprietary Windows source code (whether leaked or otherwise) from making its way to the ReactOS codebase [0]. When Windows source code leaked, in 2006, ReactOS did a complete codebase audit to ensure that it was not tainted.
"Is ReactOS legal?
Yes. ReactOS is fully legal.
Developers (devs) have not looked at Microsoft Windows™ source code. They have used the public documentation of Microsoft Windows OSes. They have made several tests to understand how Microsoft Windows works. In fact, ReactOS does the same things that Windows does but it does it differently as we don't have the same source code and it is all programmed by different developers. All code in ReactOS is released under the GNU GPL (General Public License). Is ReactOS based on Microsoft Windows™ original source code?
No! ReactOS consists only of clean-room engineered GNU GPL (General Public License) and GPL compatible licensed source code. "
> Clean room design is usually employed as best practice, but not strictly required by law. In NEC Corp. v Intel Corp. (1990), NEC sought declaratory judgment against Intel's charges that NEC's engineers simply copied the microcode of the 8086 processor in their NEC V20 clone. A US judge ruled that while the early, internal revisions of NEC's microcode were indeed a copyright violation, the later one, which actually went into NEC's product, although derived from the former, were sufficiently different from the Intel microcode it could be considered free of copyright violations.[1]
1. https://en.wikipedia.org/wiki/Clean_room_design
2. https://www.linux.com/news/reactos-suspends-development-sour...
Im definitely not taking shots at ReactOS here, I’m on their side and am fascinated with the project. You’re right I should have been clear that they shut down and has themselves audited instead of risking a court battle but I don’t think the difference matters much, either way they were gonna have a code audit to disprove these allegations. But in regards to them, there’s a lot of wrong information floating around this thread.
> claim was made on 17 January 2006 by developer Hartmut Birr on the ReactOS developers mailing list (ros-dev) that ReactOS contained code derived from disassembling Microsoft Windows.[25] The code that Birr disputed involved the function BadStack in syscall.S,[26] as well as other unspecified items.[27] Comparing this function to disassembled binaries from Windows XP, Birr argued that the BadStack function was simply copy-pasted from Windows XP, given that they were identical. Alex Ionescu, the author of the code, asserted that while the Windows XP binary in question was indeed disassembled and studied, the code was not merely copy-pasted, but reimplemented; the reason why the functions were identical, Ionescu claimed, was because there was only one possible way to implement the function